Jakob Nielson is one of the oldest and most respected name in terms of web usability and research in this field and now he has written a book titled Eyetracking Web Usability, by Jakob Nielsen and Kara Pernice of the consultancy Nielsen Norman Group. For this book what Nielsen and Pernice have done is track the eye movements of hundreds of people as they navigate websites this has led to great insight into how people interact with ads some of the key results were

People in the study saw 36% of the ads on the pages they visited.

The average time a person spent looking at an ad, though, was brief — one-third of a second.

People who were just browsing the Web looked at only 5% more ads than those trying to accomplish a specific task.

Participants in the study looked at

52% of ads that contained only text,

52% of ads that had images and text separately

and 51% of sponsored links on search-engine pages.

Ads that got a lot less attention included

Those that imposed text on top of images (people looked at just 35% of those)

and ones that included animation (it might seem movement is attention-grabbing, but only 29% of these ads garnered a look).